1. Field of the Invention
The present invention relates to a heat-treating apparatus for heat-treating objects to be heat-treated such as semiconductor wafers for oxidation, diffusion, or the like. For example, diffusion apparatus is used as such an apparatus.
2. Description of the Related Art
When, for example, semiconductor wafers are heat-treated for oxidation, diffusion, or the like, a plurality of semiconductor wafers are mounted on a quartz boat, and the boat is loaded into an heat-treating furnace, thereby performing an heat-treating process.
Such an heat-treating apparatus comprises a process tube made of a heat-resistant material such as quartz, and a heater arranged outside the process tube. An opening is formed in one end of the process tube. The boat mounting the wafers thereon is loaded from the opening into the process tube. While a gas required for heat-treating is introduced in the process tube, a power is supplied to the heater so as to heat-treat the wafers. In this heat-treating, in order to prevent the gas fed into the process tube from leaking out, the opening is capped with a proper member.
In heat-treating, since the process tube is heated to a temperature as high as 1,100.degree. C., and this capping member is also heated to a high temperature, the capping member is made of the same heat-resistant material, e.g., quartz, as that of the process tube.
In addition, various parts for loading/unloading objects to be heat-treated are arranged around the heat-treating furnace. The heat-treating apparatus is constituted by these parts and the heat-treating furnace.
A corrosive gas such as hydrochloric acid may be used as a reaction gas used for heat-treating of semiconductor wafers. In this case, if the waste gas leaks from between the process tube and the capping member and is diffused around the heat-treating furnace, the parts around the heat-treating furnace are corroded by the waste gas. Therefore, airtightness is required at a contact portion between the process tube and the capping member.
In order to prevent such gas leakage, an organic sealing member, such as rubber normally used for sealing, may be interposed in such a contact portion. However, since the process tube is heated to 1,100.degree. C., an organic sealing member cannot be used for sealing.
For this reason, sealing between the process tube and the capping member is conventionally performed by fitting between these members
Since both of the members are made of a hard heat-resistant material such as quartz, insufficient sealing may occur even by fitting. Therefore, the parts around the heat-treating furnace cannot be effectively protected against a corrosive gas.